Electronic vacuum pump



Oct. 4, 1938. L. MALTER 2,131,897

ELECTRONIC VACUUM PUMP Filed Feb. 27, 1957 H ME.

iii-Ii: 2 w 2 INV EN TOR LOU/S MAL TER BY F0 wa W flv/ ATTORNEY Patented Oct. 4, 1938,

PATENT OFFICE ELECTRONIC VACUUMI PUMP Louis Maltei', West Orange, .L, assignor, by mesne assignments, to Radio Corporation of America, New York, N. Y., a corporation of Delaware Application February 27, 1937, Serial No. 128,088

6 Eiaime.

My invention relates to apparatus for producing high vacuum in closed receptacles, such as in envelopes of electron discharge devices.

A common type of high vacuum pump, known as a diffusion p'ump, comprises a device in which one or more jets of vapor are projected along a conduit communicating with the chamber to be exhausted to entrain the gas molecules in the chamber and discharge them in the inlet of a. so-

110 called rough or backing pump which is usually a tandem connected mechanical vacuum pump. It has been proposed by Hanseli in U. S. Patent 2,022,465 to improve pumps of this type by ionizing the gas on its way to the rough pump. The

35 object 01 my invention is to increase the speed and eiiiciency of pumps of the type in which the gas is ionized.

In accordance with my invention an electrical vacuum pumpingdevice is provided with means U for increasing the probability of collision-between the ionizing electrons and the gas molecules in the chamber to be exhausted by increasing the path length of the electrons and for drawing the ionized molecules of the gas from the chamber. I5 In the preferred embodiments of my invention electrodes cooperating with an electron source are so positioned and energized that the emitted electrons aregiven an undulatory or rhythmical motion and travel to a collecting electrode along a circuitous path much longer than the distance between the cathode and the collecting electrode, or liberate secondaryelectrons to materially increase the number of electrons in the discharge space.

The characteristic features of my invention are defined with particularity in the appended claims and preferred embodiments thereof are described in the following specification and theaccompanying drawing in which Figures 1, 2 and 3 show schematically electrical pumping devices embodying the characteristic features of my invention, with means for efllciently ionizing and exhausting the gases in a chamber.

Envelope I to be exhausted and shown by way of example as the bulb of an electron discharge device, is connected through'an exhaust line or conduit 2 to a pump 3 of a type adapted to remove most of-the gas from the envelope. To speedily draw the remaining gas molecules from the envelope, I insert in the exhaust line my novel electrical evacuating device for ionizing the gas and electrostatically biasing the charged molecules toward the pump 3. My novel evacuating device comprises a chamber or container 4, prefl5 erably of metal or metal coated glass, connected at its ends to conduit 2. To ionize the gas molecules entering the chamber, cathode 5, shown by way of example, as a coiled filament, is mounted in one side of the chamber, and grid-like anode ele'ctrode or electron collector B with its upper end adjacent the inlet port of the chamber is mounted in insulated spaced relation from the filament in the chamber. With a positive potential on electrode 6, electrons emitted by the cathode are drawn to the electrode and, as explained in Hansell, supra, collide with and ionize some of the gas molecules in the space between the two electrodes.

While the precise nature of the electron phenomena in my novel device is not known, it is believed that those molecules which migrate into the electron discharge space and are ionized are violently repulsed by the positively charged electrode 6. The ionized molecules may travel at an accelerated speed in all directions from electrode 6, but because of the asymmetry of the positive electrode with respect to the inlet and outlet ports of the container, the positive electrode beingcloser to the inlet port, the majority of the ionized molecules travel outwardly and downwardly with but a few finding their way back into the inlet port. Not only does positive electrode 6 accelerate the molecules toward the outlet port, but functions as a one way trap, preventing the return of the ionized molecules from the lower regions of the container into the inlet port. To prevent the accumulation of a charge on the wall of the chamber, it may be grounded or connected to the filament.

To increase the efiiciency of ionization I propose to increase the probability of collision between electrons and molecules by directing the electrons leaving the cathode along a relatively long path, compared to the linear distance between the cathode and its collecting electrode. According to one species of my invention, the electrons are caused to oscillate in the chamber much as they do in a. conventional Barkhausen- Kurz oscillator after they leave the cathode and before they are attracted to and absorbed by the positively charged electrode. According to this species of my invention, shown in Figure l, I mount a. second grid-like electrode 1 in the chamber opposite the cathode and connect it tothe cathode through the secondary winding of transformer 8 to the cathode. Electrode 6 is connected to an intermediate point of said winding through battery 9, which is of such a potential and polarity as to maintain electrode 6 at a. rela-- tively high podtive voltage with respect to the filament. Battery ll impresses a slightly negative potential on electrode 1. Coupled to transformer l is an alternating current source I l, preferably of relatively high frequency.

After a moderately low vacuum is created in chamber I and envelope l by rough pump 3, filament I is energized to electron emitting temperature and a high frequency alternating voltage is impressed upon the electrodes. Electrons attracted by the positively charged grid I approach the grid with high velocity and pass through the mesh of the grid toward negatively charged electrode I. The combined repulsing force of negative electrode 1 and the attractive force of positively charged grid 6 on the positive molecules cause the electrons to return toward the filament through the mesh of the grid and the oscillations are continued in synchronism with the applied alternating voltage. The smaller the electron collecting area of the anode, the greater will be the number of times each electron may oscillate before being collected by the anode. According to the object of my invention, then, the mah of the anode must be quite open, presenting to the filament a relatively small area. Oscillations may of course be self-sustaining by connecting the electrodes with the proper feedback as in conventional oscillators. When the electrons follow a long oscillating path before they finally strike and are absorbed by the positive electron, it can be seen that for a given electron current the probability of collision between each electron and a molecule of gas entering the discharge space from the envelope is materially increased.

A second embodiment of my invention, shown in Figure 2 comprises means for directing the ionizing electrons in a circular path similar to that in the so-called magnetron. In the illustrated embodiment of this form of my invention a rod-like anode I2 is centrally placed in the chamber 4. Concentric with and surrounding the anode is a cathode l3 shown by way of example in Figure 2 as comprising a plurality of parallel filamentary wires arranged in a circle and attached at their ends to two current supply and supporting rings ll. Battery i5 connected between the anode and filament applies a high positive voltage to the anode. Electrons emitted by the cathode and attracted by the anode may be caused to travel in a circular path when a magnetic field of optimum intensity is introduced in the discharge space with the lines of electromagnetic force normal to the direction of travel of the electrons. Induction coil l6, connected to a direct current source, is shown positioned around chamber 4 with its axis coincidental with the anode. with an anode potential of 300 volts and a radial spacing between the anode and cathode of 2 cm. and a field intensity of 57 gauss, electrons leaving the cathode can be directed in a circular path with a diameter substantially equal to the anode-to-cathode spacing and made to travel through about 15 revolutions before striking the anode. The electrons following the long circular path between the cathode and anode of course have a much greater probability of colliding with gas molecules entering the discharge space. The ionized molecules are impelled, as explained in connection with the device of Figure 1, toward the outlet port and are pumped away by pump 3.

In a third embodiment of my invention, shown by way of example in Figure 3, a cathode l1 and grid-like anode on electron collector it are mounted in insulated spaced relation in chamher 4. In this embodiment of my invention the ionization of gas is augmented by secondary electrons supplied from an electron emissive layer coated on disc shaped electrode ll. Cathode l1, grid-like electrode l8, and disc electrode I! are connected to the terminal and intermediate taps of transformer l as described in Figure 1. Primary electrons emitted from cathode I! may be caused to oscillate in a path between the two outer electrodes, passing through the mesh of electrode I. and functioning to ionize gas molecules as described in connection with Figure 1. Those primary electrons which receive sufficient velocity in approaching positively charged grid electrode id to pass through the mesh of the grid and strike disc I! dislodge a number of secondary electrons which, like the primary electrons, are attracted by the positive grid electrode and in large numbers oscillate in the discharge space in synchronism with the impresed high frequency voltage from source ii. The primary electrons, with the aid of the secondary electrons, may reach such a number and so fill the discharge space that the probability of collision and ionization of gas molecules is materially increased.

A filamentary electron source may if desired be dispensed with and ionization initiated by suddenly applying a high voltage between the electrodes or by applying the discharge from the terminal of a spark coil to the chamber wall.

To those skilled in the art, it will be apparent that the present invention is not limited to the precise arrangements and design features exemplified, since these have merely been illustrated said source, and means to give a rhythmical motion to the electrons emitted by said source for increasing the distance of travel of electrons pass- I ing between said electron source and said anode electrode.

2. Apparatus for producing a vacuum comprising a container with an inlet port smaller than the container and an outlet port, an anode electrode positioned adjacent said inlet port, an electron source mmmted in insulated spaced relation to said anode electrode and to said inlet port in said container, means for directing elec-- trons from said electron source to said anode electrode along a path substantially longer than the distance between said anode electrode and said electron source for ionizing gas in the container.

3. Apparatus for producing a vacuum comprising a container with an inlet and an outlet port, a grid-like electrode positioned in the container nearer said inlet port than said outlet port, a cathode mounted on one side of said grid-like electrode, a cold electrode mounted on the other side of said grid-like electrode, and means for applying an alternating voltage between the cathode and said cold electrode, the areaof the grid-like electrode presented to the cathode and cold electrode being relatively small.

4. Apparatus for evacuating an envelope comprising a container with an inlet port communieating with the envelope, and an outlet port, an electrode positioned adjacent said inlet port, a filament electrode mounted in the container in insulated spaced relation to said electrode, an induction coil surrounding said container positioned to introduce in the space between the electrodes electromagnetic lines of force normal to a line between the electrodes. 2

5. Apparatus for producing a vacuum comprising a container with an inlet and an outlet port,

an electron collector adiacent said inlet port, a cathode on one side of said collector and a sheetlike electrode coated with an electron emissive layer on the other side of said collector, means for impressing a positive direct current potential on said collector, and means for impressing an alternating voltage between said cathode and sheet-like electrode.

6. Apparatus for producing vacuum in an envelope comprising a chamber with an inlet port in one end of the chamber substantially smaller than said end, and an outlet port, an exhaust tube communicating with the envelope to be evacuated and with said inlet port, an elongated anode electrode for collecting electrons central in said chamber closer to the inlet port than to the outlet port, an electron source mounted in insulated spaced relation to said anode electrode and laterally of said anode electrode, and means for giving an undulatory motion to the electrons emitted by said source and directing the, electrons along a circuitous path from the electron source to the anode electrode substantially longer than the linear distance between the source and electrode.

LOUIS MAL'I'ER. 

